Comparison of the Inhibition of Goitrogenesis in the Rat Produced by X Rays and Radioactive Iodine

Groups of six rats were treated as follows: (A) Controls; (B) 10 μc 131I intraperitoneally; (C) 30 μc 131I; (D) 500 r X rays to the thyroid; (E) 1000 r X rays to the thyroid and (F) 2000 r X rays to the thyroid. Three to four months later all groups were given an 11 -day course of propylthiouracil and killed. The average thyroid weight of the controls (A) was 54 mg, of the 10 μc 131I group (B) 46 mg and of the 500 r X rays group (D) was 48 mg. Goitrogenesis, however, was inhibited in groups (C), 30 μc 131I, the average thyroid weight being 32 mg, in group (E) 1000 r X rays, average thyroid weight 28 mg and in group (F) 2000 r X rays, average thyroid weight 27 mg. Thus 1000 rads of X rays appeared as effective as 30 μC of 131I in the inhibition of goitrogenesis. It was estimated that in the animals which received 30 μC of 131I intraperitoneally, the mean thyroid dose lay between 10,000 and 15,000 rads with a range within the gland extending approximately from 2000 to 24,000 rads.